This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Our goal in this project is to develop and test protein force ?elds that ?t into the constraints of Anton (i.e. that employ simple functional forms and ?xed-charge models for electrostatics) while providing improved energetic and structural ?delity to the underlying protein energy landscape. In this way, we can help to ensure that the next round of Anton allocations will pay greater scientific dividends by providing a better understanding of the strengths and limitations of the force ?elds being used, and by providing access to new force ?elds with improved properties. Force fields based on Amberff99SB, but with new backbone and side-chain torsion parameters, and new atomic charges, will be tested on four protein systems, in both solution and crystalline environments.